Among all of the nucleic acid components, guanine nucleotides are unique in their ability to form regular ordered structures in aqueous media. The self-association process is dependent on the nature of the alkali metal ion counter ion, the position of the phosphate moiety of the ribose ring, the pH of the medium, concentration, and temperature. Our nuclear magnetic resonance studies have demonstrated that the ordered form of Na ion 2 (5'-GMP) in homogeneous solution is an octamer consisting of two stacked planar tetramer units formed in part by hydrogen binding between donor-acceptor positions on the purine ring. Complexation of Na ion at two different binding positions is essential in achieving structural stability. One binding site is located at the center of the O(6) hole of the tetramer units. This primary binding site is Na ion-specific and structure directing. The secondary site involves chelation of the metal by two phosphate oxygens on adjacent tetramers. The secondary site is not metal ion-specific. The replacement of Na ion by K ion leads to dramatically different ordered forms of the nucleotide, the structures of which are currently under investigation. To our knowledge, these alkali metal-nucleotide systems represent the first examples in which specific alkali metal ion complexation plays a principal structure directing role in the solution ordering of a nucleotide.